<template>
    <div
        class="back-to-top"
        @click="backToTop"
        v-show="showReturnToTop"
        @mouseenter="show"
        @mouseleave="hide"
    >
        <i
            :class="[ bttOption.iClass ]"
            :style="{ color:bttOption.iColor, 'font-size':bttOption.iFontsize }"
        >
        </i>

        <span
            class="tips"
            :class="[ bttOption.iPos ]"
            :style="{ color:bttOption.textColor }"
            v-show="showTooltips"
        >
            {{ bttOption.text }}
        </span>
    </div>
</template>

<script>
    import { scrollIt } from '../assets/javascript/scrollIt.js'

    export default {
        name: "BackTop",
        props: {
            text: { // 文本提示
                type: String,
                default: '返回顶部'
            },
            textColor: { // 文本颜色
                type: String,
                default: '#ff0000'
            },
            iPos: { // 文本位置
                type: String,
                default: 'right'
            },
            iClass: { // 图标形状
                type: String,
                default: 'fa fa-arrow-circle-up'
            },
            iColor: { // 图标颜色
                type: String,
                default: '#ff0000'
            },
            iFontsize: { // 图标大小
                type: String,
                default: '32px'
            },
            pageY: { // 默认在哪个视图显示返回按钮
                type: Number,
                default: 400
            },
            transitionName: { // 过渡动画名称
                type: String,
                default: 'linear'
            }
        },
        data: function () {
            return {
                showTooltips: false,
                showReturnToTop: false
            }
        },
        computed: {
            bttOption () {
                return {
                    text: this.text,
                    textColor: this.textColor,
                    iPos: this.iPos,
                    iClass: this.iClass,
                    iColor: this.iColor,
                    iFontsize: this.iFontsize
                }
            }
        },
        methods: {
            show () { // 显示隐藏提示文字
                return this.showTooltips = true;
            },
            hide () {
                return this.showTooltips = false;
            },
            currentPageYOffset () {
                // 判断滚动区域大于多少的时候显示返回顶部的按钮
                window.pageYOffset > this.pageY ? this.showReturnToTop = true : this.showReturnToTop = false;

            },
            backToTop () {
                scrollIt(0, 600, this.transitionName, this.currentPageYOffset);
            }
        },
        created () {
            window.addEventListener('scroll', this.currentPageYOffset);
        },
        beforeDestroy () {
            window.removeEventListener('scroll', this.currentPageYOffset)
        }
    }
</script>

<style scoped lang="scss">
    .back-to-top {
        position: fixed;
        bottom: 5%;
        right: 100px;
        z-index: 9999;
        cursor: pointer;
        width: auto;
        i {
            font-size: 32px;
            display: inline-block;
            position: relative;
            text-align: center;
            padding: 5px;
            /*background-color: rgba(234, 231, 231, 0.52);*/
            border-radius: 5px;
            transition: all 0.3s linear;
            &:hover {
                border-radius: 50%;
                background: #222;
                color: #fff !important;
            }
        }
        .tips {
            display: inline-block;
            position: absolute;
            word-break: normal;
            white-space: nowrap;
            width: auto;
            font-size: 12px;
            color: #fff;
            z-index: -1;
        }
        .left {
            right: 0;
            top: 50%;
            margin-right: 50px;
            transform: translateY(-50%);
        }
        .right {
            left: 0;
            top: 50%;
            margin-left: 50px;
            transform: translateY(-50%);
        }
        .bottom {
            bottom: 0;
            margin-top: 50px;
        }
        .top {
            top: 0;
            margin-bottom: 50px;
        }
    }
</style>
